Liver transplantation (LT) is a unique model to study hepatitis C virus (HCV) entry into hepatocytes. Recent in vitro studies suggest significant changes in the expression of the HCV receptors claudin-1 and occludin after HCV infection.In 2011 our aims were: (1) to characterize claudin-1 and occludin expression in grafts from LT recipients and (2) to explore their potential influence on early HCV kinetics and their changes after HCV infection. We included 42 HCV-infected LT recipients and 19 uninfected controls. Claudin-1 and occludin were detected in paraffin-embedded liver biopsies obtained during reperfusion and 3 and 12 months after LT. HCV receptors were characterized by confocal immunofluorescence microscopy;quantification and colocalization studies were performed with dedicated software. Claudin-1 and occludin expression were restricted to the apical pole of hepatocytes. There was a significant correlation between the amount of scavenger receptor B1 at the time of reperfusion and the HCV-RNA decay during the first 24 hours following LT (r = 0.55, P = 0.007). Similarly, there was a significant correlation between the levels of claudin and occludin and the slope of HCV-RNA increase during the first week after LT (r = 0.63, P = 0.005). Occludin and claudin-1 levels increased significantly 12 months after LT (P = 0.03 and P = 0.007, respectively). The expression pattern of both proteins, however, remained unchanged, colocalizing strongly (60%-94%) at the apical membrane of hepatocytes. CONCLUSIONS: HCV receptor levels at the time of LT seem to modulate early HCV kinetics. Hepatitis C recurrence after LT was associated with increased levels of claudin-1 and occludin in the hepatocyte cell membrane, although it did not alter their localization within the tight junctions. In fiscal year 2011 we also participated in microarray studies comparing hepatitis C and E infections in experimentally infected chimpanzees and we studied neutralizing antibodies in hepatitis C patients and perinatally infected children.